Smart 'stat modulation

[MarkyG82]

Need to choose one of two system boilers (Worcester 4000 or glow worm energy 7). I want modulation for all the obvious reasons. I also want smart controls so we can add smart TRVs upstairs to zone off the area. Currently not possible to zone it the manual way due to existing plumbing.

So I've come up against the issue that neither boilers are opentherm and the thermostats we like (tado or nest) don't modulate without it. Plumber has done some homework and thinks that adding weather compensation will take care of the modulation while allowing the smart controls to call for heat via relay.

 

Two questions to you knowledgeable folk:

1) Is my plumber right?

2) Will the call for water cylinder heating also be affected by said weather compensation? 

 

On point 2, the glow worm has a heat setting Dedicated to hot water if that makes a difference.

 

Last question:

3) Do you know of a smart thermostat system (with TRVs) that can natively modulate central heating output using the above boilers?

 

Thanks 

[JohnMo]

Why limit yourself to those boilers.

 

Just get a decent combi, Atag, Intergas Viessmann. If the boiler isn't opentherm equipped as standard move on to another boiler.

 

You need to configure the system as priority demand hot water or X plan. Then have the heating on weather comparison and when cylinder calls for heat the boiler runs at high temperature.

 

The ones I mentioned above do it out the box. 

 

You can get a standard kit to convert any opentherm boiler to X plan.

 

https://www.ephcontrols.com/section/pdhw/

 

Really do you need or just want smart controls? You want good quality trv's with remote sensing, so they measure room temp, not the temperature at the radiator. Tado do not modulate boiler unless you buy the European model, ones sold in UK trade outlets are on off only.

[MarkyG82]

@JohnMo

Thanks. The boiler selection is based on what the plumber is supplying. I will question that as it may help like you suggest.

 

The smart bit is definitely a want but it will allow us to zone off the upstairs. We like a cold bedroom. I'm happy to set up remote sensing. I already have stuff in the house that will do it. Just needs setting up in home assistant.

 

Are you suggesting that a well set up opentherm boiler will put perform the weather compensation hack as per the plumbers suggestion?

[JohnMo]

Not sure why you need additional relays, think you may be thinking along the wrong lines. Blasting the whole house with high temperature heat is just not efficient, to operate you need thermostats everywhere to control over and under temperature swings. Bit like driving a car with full throttle and idle only.

 

Weather compensation will just supply the house with enough energy to match the energy being lost to the outside world.  So the boiler runs for long periods at a low flow temperature. Efficiency gains are in the order of 20 to 30% (less gas usage). Boiler efficiency goes from 80ish to 110%.

 

So only use the boiler manufacturer controller for the main part of house, it will have a time schedule and different temperature profiles, and then TRVs on the bedroom rads.

 

Basically set the WC curve, manufacturer manual will give you a start point on that, add room compensation feature also (setting inside the controller), this will fine tune the settings based on what really happens in the house and may also optimise the start and stop timings. Set the schedule to give you temp you want and setback 2 to 3 degrees only at night. Use the trv's to get the bedroom temps where you want.

 

You really don't need any smart controls, let the boiler control manage it all.

 

 

[SimonD]

10 hours ago, MarkyG82 said:

1) Is my plumber right?

 

Not quite. With the Worcester controls, you'll use something like the EasyControl with the Worcester smart trvs to achieve modulation. In this instance you'll get the Easycontrol to turn the boiler on/off with modulation and just use the trvs to control room temp via flow control to rads not boiler control. As soon as you try to add multi-zoning using 230v relay on a Worcester you lose the modulation capability. IMHO the whole design of Worcester controls is pretty flawed and technical support for the controls is a bit random. You can't use Tado or Nest with a Worcester unless you're happy with relay control, which defeats the whole purpose. You'll also need the hot water diverter kit to be installed to provide priority hot water with the 4000.

 

With regards to Glow-worm, it's essentially a Vaillant, so you're better off considering Vaillant/Glow-worm controls as they're ebus - they're better than the Worcester, but you're stuck with what they've got.

 

TBH, just like @JohnMo says, there are plenty of other boiler options out there that can do a better job. ATAG are now offering 18 year warranties on boilers, so well worth a look. Even an Ideal Vogue Max will be opentherm with 12 year warranty with a max accredited installer, so can be set up PDHW with the EPH priority hot water kit and the Ideal own brand Halo Heat & System also supports PDHW (but as I've found with a couple of installs the Halo is a bit buggy and tech support doesn't fully understand it all). Otherwise Viessman is a good option too.